Recently, introduction of electricity generation by renewable energy such as sunlight and wind has been in progress. However, there are problems; for example, the amount of electricity generation considerably fluctuates depending on the strength of wind or the intensity of sunlight, and electricity generation at night is impossible. It is feared that these problems influence on an electric power system. Accordingly, efficient and stable electricity supply adapted to large-scale renewable energy electricity generation has been demanded.
Systems that use renewable energy to efficiently and stably supply electricity include a power plant that uses solar heat.
This power plant uses a solar heat collector to collect solar heat. The power plant feeds the collected heat to a heat exchanger via a heat medium, and changes water into steam by the fed heat. The power plant drives a turbine by the steam and thereby generates electricity.
The heat collected by the solar heat collector can be accumulated by a heat accumulator via the heat medium. The accumulated heat is again fed to the heat exchanger through the heat medium, for example, during night hours when solar heat cannot be collected, so that electricity can be generated. This makes it possible to eliminate the problem of unstable electricity supply which is feared in electricity generation that uses renewable energy.
The following condition needs to be satisfied in order for the power plant that uses solar heat to drive the turbine for efficient electricity generation. This condition is that the temperature of the heat medium supplied with the heat collected by the solar heat collector is greater than or equal to a predetermined temperature and that the flow volume of the heat medium is greater than or equal to a predetermined flow volume.
However, sufficient heat cannot be collected by the solar heat collector because of various factors such as weather, temperature, humidity, and wind, so that the temperature of the heat medium may not become greater than or equal to the predetermined temperature or the flow volume may not become greater than or equal to the predetermined flow volume. Under these circumstances, for efficient electricity generation, it is necessary to feed the heat accumulated by the heat accumulator to the heat medium, or secondarily heat the heat medium by a boiler. In this case, heat that can be used for electricity generation at night is reduced, and further energy is needed to drive the boiler. Therefore, it is not possible to enjoy the benefits of the use of the solar heat to drive the turbine.